Environmentally hazardous fluids such as acids, oils, and toxins which can cause serious harm to the environment often need to be pumped through fluid flow systems from one location to another. When pumping such dangerous fluid materials, it is important that neither the liquid nor the gases which are often released by the liquid being pumped escape into the surrounding atmosphere or pump areas outside of the desired fluid pumping path.
Heretofore, conventional mechanical seals have been developed in order to overcome rotating pump shaft sealing problems. Such prior art mechanical seals allow for a fairly secure seal along the pump shaft against the fluids being pumped so as to prevent them from leaking or escaping axially rearward along the shaft. Yet, in some cases, the hazardous fluids being pumped penetrate the seals when the pressure within the pump becomes too high for the seals to handle or by other failure modes thereby allowing the fluid to escape into the surrounding environment and/or rearwardly along the pump shaft toward the pump motor area.
Double seal arrangements, including a barrier fluid disposed therebetween, are known in the art. In such arrangements, two seals form a cavity which is filled with a clean or environmentally safe barrier fluid. The seal facing the excess hazardous liquid being pumped inhibits movement of the pumped liquids sufficiently to prevent penetration of the seal by the liquid. Vapor produced by the liquid which permeates the first seal is stopped by the barrier fluid located in the barrier chamber defined between the seals. Unfortunately, if the first of these two seals breaks, the barrier fluid is permitted to escape from the barrier chamber, in effect, leaving the second seal without lubrication and quickly effecting failure of that second seal and allowing the harmful gases and liquid to penetrate the second seal and reach the surrounding environment. Furthermore, if the second seal fails first, the barrier liquid will be lost to atmosphere and the same end result is effected. If the first seal fails, the harmful liquid often easily penetrates the second seal thereby creating both hazardous gas and liquid leakage.
FIG. 1(a) is a cross-sectional side elevational view of a typical prior art chemical processing pump 1. Pump 1 includes casing 3, impeller 5, rotating pump shaft 6, annular stationary member 9, inboard ball bearings 11, outboard ball bearings 13, annular seal gland 15, pump frame 17, outboard bearing locknut 19, annular outboard bearing cover 21, pump shaft key coupling 23, seal 25, seal 27, seal 29, adapter 31, and mounting member 33. Pump 1 in FIG. 1(a) is shown in an inverted position for consistency of viewing.
Pump 1 also includes a motor (not shown) affixed to shaft 6 by way of key coupling 23. The motor functions to drive shaft 6 thereby rotating impeller 5 so as to pump fluid between inlet 35 and outlet 37 thereby defining a centrifugal pump.
FIG. 1(b) is a side elevational view of another prior art chemical processing pump, this view illustrating a partial section of the pump when cut in half. This pump includes impeller 5 for pumping fluid between fluid inlet 35 and fluid outlet 37. Also disclosed are inboard bearings 11, outboard pump shaft bearings 13, heavy duty rotatable pump shaft 6 for driving impeller 5, interchangeable bearing cartridge 4, stainless steel shaft sleeve 8 surrounding pump shaft 6, packing or mechanical seal 27, two piece packing gland 26, and support 33. This particular drawing is a typical section of a Worthington D line ANSI centrifugal pump.
Gland 26 and seal arrangement 27 of the FIG. 1(b) pump located adjacent member 9 are often not strong or effective enough to prevent the fluid being pumped from leaking rearward along shaft 6 from impeller 5 and reaching the rear pump areas or surrounding atmosphere.
Heretofore, the sealing arrangements used in area 36 of conventional chemical processing pumps have been inadequate for the aforesaid reasons as well as those discussed below. Typically, a pair of annular mechanical seals are disposed along shaft 6 in area 36 between inboard bearing 11 and impeller 5. Unfortunately, many operating conditions and liquid characteristics have been found to cause prior art sealing arrangements to prematurely break down thereby causing leakage of the fluid (liquid and/or gas) being pumped into the surrounding environment.
It is apparent from the above that there exists a need in the art for a seal arrangement for a pump which is less sensitive to surrounding changes in temperature and pressure as well as both fluid and operating conditions thereby creating a more environmentally safe pump. It is preferred that such a seal arrangement be simple, economical, and environmentally safe.
U.S. Pat. Nos. 5,261,676 and 5,340,273, commonly assigned, disclose an environmentally leakproof pump which is prior art to the instant invention due to offers of sale more than one year before the instant filing date. While these patents disclose an excellent high performance pump and corresponding seal arrangement, the particular details of these prior art pumps are not felt to be material to the instant invention. Additionally, commonly owned U.S. Ser. Nos. 08/200,012 (filed Feb. 22, 1994) and 08/214,288 (filed Mar. 17, 1994) are related to the instant invention in that they disclose pump sealing systems including barrier fluid circulation systems.
It is the purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.